Who knows how much more they are tacking on the price, if they even are upping the price because it's your dad's old car. Like someone mentioned, who knows what the market is like over there for these cars. Only thing I know for sure is that there are not many of those cars in Japan vs over here.
If it were me, as mentioned before, the car being your dads's old car, it is priceless. If you can afford it, go for it. You wouldn't want to have any regrets or thoughts like, "Yeah, I found my dad's old Challenger T/A but I didn't feel like spending the extra $$$ to get it back." and kick yourself for the rest of your life. Your dad only had this one Challenger T/A and if it's something really special, go for it.
One Debbie Downer thing to mention though as far as transporting it: I guess I would be really worried about people potentially taking it for joyrides or messing with it. Make sure you go with a very reputable company. There is a member here (Sledge Hammer) that sold his Challenger to someone I think in France and the car ended up getting stolen by people who worked the docks. Not trying to scare you but just want to to be careful.
It's a beautiful car. Hope all works out for you and you'll be happy.